#include <iostream>
#include <fstream>
#include <stack>
#include <vector>
using namespace std;

ifstream f ("ctc.in");
ofstream g ("ctc.out");

const int NMAX = 100000;
int N, M, nrc;

vector<int> G[NMAX+1], CTC[NMAX+1];
int D[NMAX+1], Dmin[NMAX+1], Timp = 0;

stack<int> S;
bool inSt[NMAX+1];

void citire() {
    int x, y;
    f >> N >> M;
    for (int i=1; i<=M; i++) {
        f >> x >> y;
        G[x].push_back(y);
    }
}

void DFS(int x) {
    D[x] = ++Timp;
    Dmin[x] = D[x];
    S.push(x);
    inSt[x] = 1;
    //
    for (const auto &y : G[x]) {
        if(D[y] == 0) {
            DFS(y);
            Dmin[x] = min(Dmin[x], Dmin[y]);
        } else {
            if (inSt[y] == 1)
                Dmin[x] = min(Dmin[x], D[y]);
        }
    }
    //
    if (Dmin[x] == D[x]) {
        int u;
        nrc++;
        do {
            u = S.top();
            CTC[nrc].push_back(u);
            S.pop();
            inSt[u] = 0;
        } while(x != u);
    }
}

void afisare() {
    g << nrc << '\n';
    for (int i=1; i<=nrc; i++) {
        for (const auto &x : CTC[i])
            g << x << ' ';
        g << '\n';
    }
}

int main(){
    citire();
    //
    for (int i=1; i<=N; i++)
        if(D[i] == 0)
            DFS(i);
    //
    afisare();
    f.close();
    g.close();
    return 0;
}